1. Field of the Invention
This invention relates to substrate for paperboard packaging having an internal sizing agent applied to the paperboard. Internal sizing agents add moisture resistance to the paperboard and, generally, reduce edgewicking in the paperboard. Edgewicking is an undesired occurrence in aseptic liquid packaging and cupstock where liquid penetrates through an internal cut edge of the package or cup, and may weaken the package.
2. Description of the Related Art
Paper machine systems are typically classified as acidic or alkaline, depending on the pH of the pulp slurry provided to the machine. Whether the system is acidic or alkaline will determine what sizing agents may be used in the furnish or on the machine for adding liquid resistance to the paperboard. For acidic systems, a dispersed rosin sizing (“DRS”, or “rosin”) may be used. For alkaline systems, alkylketene dimer (AKD) may be used, but more systems utilize alkenylsuccinic anhydride (ASA) instead. ASA may also be used in acidic systems.
The ability of sizing agents to attach to cellulose fibers is an important factor in the effectiveness of the sizing agents. The direct to cellulose sizing mechanism of ASA is superior to rosin, and is without certain negative attributes associated with the use AKD.
Adding more sizing agent, up to a point, will improve the liquid resistance (e.g. edgewicking) behaviour, but at additional expense.